This invention relates to brushless DC motors and, in particular, to switching circuits of such motors to enable the control of reverse rotation.
A brushless DC motor has been known which comprises a permanent magnet rotor, a stator having a plurality of magnetic pole pieces on which windings are mounted, and a switching circuit for switching the feed of DC current to the windings in response to outputs of a plurality of detectors which are mounted in the stator at respective spaces between adjacent pole pieces.
As switching elements, transistors, micro-switches and other switching elements are used. They are connected between respective windings and a common DC power source, and are controlled by respective detectors to sequentially excite the windings in order of the rotational direction. Thus, the rotor is rotated in the direction desired. Magnetic, electrostatic or optical detection is employed for detecting the rotational angular position of the permanent magnet rotor.
The brushless DC motor is advantageously used as a motor in record players, tape recorders and so on, because of its long life time, excellent performances such as high S/N ratio and others and no-relation to the frequency of the power source. But it has a fault that a reverse rotation is not simply realized.
The reverse rotation is required in tape recorders and is used for a braking force in record players as well as tape recorders.
Accordingly, a brushless DC motor which is able to change the rotational direction with a simple construction is desirable.